What is Rec. 709?
REC. 709 is a standard color space for video displays (i.e. HD TVs, computer monitors, field monitors, projectors.) Cameras can shoot natively in Rec. 709 , however the format is not if you want to perform color correction or color grading in post production. Rec. 709 is best to regard Rec. 709 the color space you want to use for final delivery, not for video capture. If you start color grading Rec. 709 footage, you will notice rather quickly that it doesn’t offer much room to push luminance and color values.
Higher end cameras can shoot in color profile called LOG. This picture format captures a wider tonal range. It is a better option and can easily be converted to REC. 709 later with a LUT or after professional color grading and proper render settings.